In local area network (LAN) systems, 25 unshielded twisted pair (UTP) wire systems are widely accepted and used for data and voice transmission. The UTP systems are used because of their low cost and new low noise multi-pair cable design advances. Increased demands on networks using 25 pair UTP systems, including transmission rates, have forced the industry to develop higher system performance standards, such as Electronic Industry Association (EIA) Commercial Building Telecommunication Building Wiring Standards 568A Category 5 level performance. The EIA 568A Category 5 level performance defines electrical parameters for proper data signal systems that require up to 100 Megahertz frequency band width, i.e., Fast Ethernet 100Base-T.
The 25 pair systems allow LAN systems to be easier to manage with the use of 25 pair connectors and 25 pair cables. These 25 pair connectors and cables were originally used for simple telephone service and low speed network systems. However, now such connectors and cables are being considered for use with high speed data systems, as an option. With the increase in LAN data rates, system noise, especially near end crosstalk (NEXT) has also increased.
In data transmission, the received signal will include the transmission signal which is modified by various distortions. The distortions are added by the transmission system, along with unwanted signals inserted into the signals between the transmission point and the reception point. These unwanted signals are referred to as noise. The noise is a major limiting factor in the performance of communication systems. Noise can cause data errors, system malfunctions, and loss of the actual wanted signals. One type of noise is crosstalk noise, which occurs when a signal energy from one line is coupled to another victim line.
Crosstalk can occur when one transmission pair is next to another transmission pair. The capacitive (electric) or inductive (magnetic) fields generated by each transmission pair couple one transmission pair to the other transmission pair.
Crosstalk can be minimized in communication systems by decreasing signal power, increasing the distance between signal lines, providing shielding between signal lines and twisting the wires of each signal pair.
In differential signaling communication systems, plugs such as the AT&T 25 pair Category 5, the EIA 568A T568B (AT&T) 4 pair and the EIA 568A T568B (ISDN) 4 pair Category 5 have defined pin contact assignments. The defined contact layouts produce unwanted crosstalk noises. However, contact reformation to reduce crosstalk is not an option. EIA plugs T568B and T568A 8-pin plug assignments and other similar plugs are not designed for high frequency use. These plugs produce crosstalk since the contacts or terminals are adjacent as a result of the standardized plug design.
Using the standard plug designs causes crosstalk to increase as speeds or system transmission frequencies increase. Crosstalk generated in the cable is minimized by the transposition or twisting of the transmitting pair wires. However, as the signal travels through the untwisted portions of the circuit, such as the plugs and plug contacts, the capacitive and/or inductive coupling occurs to create crosstalk.
In a differential balance two wire per pair transmission signal, the signals traveling along each wire (media) are equal in amplitude, but opposite in phase. The phase difference of the two signals is .+-.n radian, or voltage=+1(E1)=-voltage-1E(E2), under ideal conditions. These signals, at any instantaneous time, couple electric and/or magnetic fields to adjacent lines, thereby reducing the signal to noise (S/N) ratio. The unacceptable S/N ratio depends on the type or quality of the services required by the system. To remove noise components, a signal equal, but opposite to, the original signal is induced. According to Fourier's wave theory and Maxwell's theory of electromagnetic fields, the coupling of the opposite phase of the transmitted signal to the previously coupled adjacent line signal causes the two signals to cancel each other completely to remove the noise from the adjacent line. This concept is employed in U.S. Pat. No. 5,432,484 to Klas et al, and U.S. Pat. No. 5,414,393 to Rose et al, the subject matter of which are incorporated herein by reference.
In 25 pair connecting hardware, multiple pairs are employed for data signal transmission. The worse case or unwanted coupling effect in the 25 pair or RJ21 plug is different from that in the 4 pair or 4 pair type plug. The worse case near end crosstalk noise in the 4 pair plug creates a balance coupled noise, that is, the noise is coupled equally upon the adjacent pairs. For an EIA T568B 4 pair plug, the worse case noise is typically between pair 1 (pins 4 and 5) and pair 3 (pins 3 and 6). In some 25 pair plugs, the worse case noise is typically between pair 1 (pins 1 and 26) and pair 2 (pins 2 and 27). The 25 pair plug can create unbalanced NEXT noise, i.e., the noise is coupled stronger upon one wire per pair than on the other wire of that pair.
Low noise EIA Category 5 connector designs have used one sided signal compensation methods. While these methods are good for interfaces or single interface design connectors, such methods will not provide Category 5 electrical performance for an interface system of two different plug modules, such as for a 4 pair connector to a 25 pair connector. Thus, an interface is needed which will reduce unwanted near end crosstalk noises created in the use of two different connectors on a single interface, for example using a 4 pair plug system and a 25 pair plug system.